JP2002118371A - Connecting structure of fiber-reinforced plastic mold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a connecting structure of a fiber-reinforced plastic mold which strongly holds connection to other part through a boss molded integrally with the mold while continuation between connected parts is allowed, related to a fiber-reinforced plastic mold excellent in a mechanical characteristics such as strength and rigidity and electromagnetic wave shielding characteristics. SOLUTION: The connecting structure is provided for the fiber-reinforced plastic mold where a thermo-plastic resin contains a reinforced fiber comprising carbon fiber. Here, the following conditions are provided: [A] the weight- averaged fiber length of carbon fiber contained in the mold is 0.1-1.0 mm; [B] the wall thickness of the mold is 0.6-5.0 mm; [C] the volume-specific resistance of the mold is 102 Ω.cm or less while the surface resistivity is 104 Ω/sq or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molded member made of fiber reinforced plastic housing for accommodating an electronic device such as a notebook personal computer, a digital camera or a mobile phone, for example. The present invention relates to a fastening structure of a fiber-reinforced plastic molded product, which enables two or more housing members to be connected to each other, or a housing member and another member to be externally and / or internally provided in the housing.

[0002]

2. Description of the Related Art As is well known, as a housing material for housing electronic equipment such as a notebook personal computer,
Fiber reinforced plastics have been widely used. The fiber reinforced plastic has an advantage that a molding method excellent in productivity and design freedom such as injection molding can be performed, and a molded product excellent in mechanical properties such as rigidity and strength can be obtained.

[0003] In particular, when carbon fiber is used as a reinforcing fiber, rigidity and strength are further improved. In addition, since carbon fiber is a conductive material, the carbon fiber exhibits a conductive property as a molded product, and a high electromagnetic wave shielding property is obtained. Demonstrate the characteristics. When using long fiber type carbon fiber as the reinforcing fiber,
Its performance is further improved as compared with the case where a conventional short fiber material is used.

[0004] In a plastic housing for housing an electronic device such as a notebook personal computer, two or more housing members are fastened to each other, and the housing and members provided inside and outside the housing. Is firmly fastened to withstand loads during product assembly and use,
In addition, it is necessary to stably hold for a long time.

FIG. 2 is a perspective view showing a fastening structure of a conventional plastic electronic device housing. In FIG. 2, reference numeral 1 denotes a molded plastic casing, into which a metal nut 3 having an internal thread is internally press-fitted into a lower hole of a cylindrical boss 2 integrally formed with the casing, and a fastening member is provided. By fastening a metal external thread 5 to the internal thread via the female thread 4, it is firmly fastened and held.

Further, according to the fastening structure of the metal nut press-fitting method, when the casing molded product is a conductive material such as carbon fiber reinforced plastic or plastic containing metal filler, the casing molded product is formed by the following route. And electrically conductive with the conductive fastening member, and the members to be fastened can be made to have the same potential, which contributes to the electromagnetic wave shielding property and the static electricity non-charging property.

Conductive housing → Integrally formed boss → Metal nut → Metal screw → Tightening member As described above, in the metal nut press-fitting type fastening structure, two or more members are firmly fastened and held, and The performance that enables conduction between the conductive members is high.

However, recent electronic equipment products are rapidly becoming thinner and lighter, and in the metal nut press-fitting method, it is necessary to increase the outer diameter of the boss to be press-fitted. Is squeezing the containment space. Also,
In order to reduce product weight, it is also required to reduce the weight of the metal nut itself.

In terms of cost, in order to fasten by the metal nut press-fitting method, the same number of metal nuts as the number of fastening points are required, and a heat press-in step of the metal nut is also required. Causes a rise in housing manufacturing costs.

[0010] When the casing material is recycled after use as an electronic device product, the product is disassembled into individual parts, the casing is collected from the components, crushed, re-compounded, and recycled. use. However, if the metal nut is still pressed into the boss of the housing,
Metal nuts must be removed before grinding because they cannot be recompounded. This step of removing the metal nut is troublesome and expensive, and is not preferable.

Therefore, at present, the self-tapping method has begun to be used instead of the metal nut press-fitting method. FIG. 3 is a perspective view showing a fastening structure of a plastic electronic device housing by a general self-tap method. In the figure, in the self-tapping method, a female screw is simultaneously formed in a lower hole of the boss 2 by directly screwing a self-tapping screw 6 having a screw on an outer diameter into a lower hole of the boss 2, and a metal nut is separately provided. It is possible to fasten two or more housing members, and to fasten the housing to members that are to be housed or housed inside the housing without the need for insertion. This method solves the problem of weight reduction, cost, and recycling in the metal fitting press-fitting method.

However, in this method, since the member holding the male screw is made of plastic, the mechanical fastening performance required at the time of assembling and using the product is satisfied as compared with the metal nut press-fitting method. Is difficult. The fastening performance generally includes the following performance.

Tightening torque: 20 N · cm or less Breaking torque: 30 N · cm or more Return / set tightening torque ratio: Torque ratio 0.5 or more Pull-out load: 500 N or more The tightening torque is the minimum torque required to tighten the screw, and the smaller the tightening torque, the easier it is to tighten with a small screwdriver. Breaking torque is the torque when the boss or thread breaks and stops functioning as a screw when the screw is continuously tightened. The greater the breaking torque, the more the boss can be prevented from being broken due to excessive tightening torque during assembly. The return / set tightening torque is the return torque that is the torque remaining when the screw is returned to the loosening direction after 24 hours at room temperature after tightening with the set torque that is larger than the tightening torque and smaller than the breaking torque. This is the ratio with the tightening torque. The larger the return / tightening torque ratio, the longer the firm fastening can be maintained. The pull-out load is a load required to pull out the screw in the vertical direction after tightening with the set tightening torque. The larger the pulling load, the more the destruction of the fastening structure due to the external force applied to the screw or boss after fastening can be prevented. Tightening /
The number of repetition endurance times of repetition is the number of endurance times indicating how many times continuous repetition of tightening and reversion can be performed by the set tightening torque before the fastening structure is broken. The greater the number of repeated tightening / returning durability, the higher the screw tightening durability during the assembly process and repair.

[0014] In order to improve such fastening performance, attempts have been made to improve the material and structure. For example, JP-A-10-265666 describes a resin composition that improves the self-tapping property in terms of material. Although the self-tapping property of the resin composition is improved, the resin composition is insufficient in tensile strength and flexural modulus and does not have electrical conductivity as a housing application requiring thinness and electromagnetic wave shielding properties. Japanese Patent Application Laid-Open No. Hei 10-93258 describes a mounting structure for improving self-tapping properties. Although the self-tapping property is improved with this mounting structure, conductivity cannot be obtained.

[0015]

SUMMARY OF THE INVENTION In view of the above-mentioned drawbacks of the prior art, the present invention provides a molded article used for a housing of an electronic device made of fiber-reinforced plastic, which has excellent strength and rigidity while maintaining moldability. It is another object of the present invention to provide a fastening structure of a fiber-reinforced plastic molded article having excellent electromagnetic wave shielding properties by enabling conduction between parts to be fastened.

[0016]

The present invention employs the following means in order to solve the above problems. That is, the fastening structure of the fiber-reinforced plastic molded product of the present invention is formed in the pilot hole of the boss integrally molded as a part of the fiber-reinforced plastic molded product in which the synthetic resin contains at least the reinforcing fiber composed of carbon fiber. The self-tapping screw has a structure capable of directly tightening and fastening with another member, and is characterized by simultaneously satisfying the following conditions [A], [B] and [C].

[A] The weight-average fiber length of the carbon fibers contained in the molded article is in the range of 0.1 to 1.0 mm.

[B] The molded product has a thickness of 0.6 to 5.0 m.
m.

[C] The molded product has a volume resistivity of 10 ² Ω.
・ Cm or less and the surface resistivity is 10 ⁴ Ω
/ Sq or less.

Further, in addition to the above structure, a self-tapping screw is directly screwed into a pilot hole of a boss integrally molded as a part of a fiber-reinforced plastic molded product, so that it can be fastened to another member. Then, the following [D] and [E]
Characterized by the following conditions:

[D] The ratio d / a of the prepared hole diameter d of the boss for tightening the self-tapping screw to the nominal diameter a of the screw is 0.70 to 0.70.
0.95 and the tip of the thread is in contact with the core layer of the boss.

[E] The ratio L / a of the screwing depth L at which the self-tapping screw is in contact in the axial direction of the prepared hole of the boss for tightening the self-tapping screw to the nominal diameter a of the screw is 1.0. ~
Within the range of 10.

The ratio D / a between the outer diameter D of the boss for tightening the self-tapping screw and the nominal diameter a of the screw is 1.3 to 5.
It is characterized by being within the range of 0. Further, the carbon fiber content of the molded article is in the range of 5 to 40% by weight. The self-tapping screw is characterized in that the volume specific resistance is within a range of 1 Ω · cm or less and the surface resistivity is within a range of 10 ² Ω / sq or less. Further, the molded article is made of a fiber-reinforced thermoplastic resin. Also, the boss for tightening the self-tapping screw has a chamfered or counterbored shape at the tip of the prepared hole. Further, the molded article houses the electronic device inside.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a sectional view of a fastening structure for a fiber-reinforced plastic molded product according to the present invention. FIG. 1 shows a fiber-reinforced plastic molded product 20 including a boss 7 integrally molded and a self-tapping screw 21. And a fastening member 22.

The fiber-reinforced plastic molded product 20 has a high-strength and high-elasticity core layer 9 in which the reinforcing fibers 8 are oriented at a high density, and a resin component density with respect to the reinforcing fibers 8 higher than that of the core layer 9. The core layer 9 has a skin layer 10 on both sides of the core layer 9. Each of the core layer 9 and the skin layer 10 includes a matrix resin containing reinforcing fibers made of carbon fibers.

As the matrix resin, a thermosetting resin can be used, but a thermoplastic resin which has excellent impact resistance and can be injection-molded with high productivity is preferable. For example, in addition to polyesters such as polyethylene terephthalate, polybutylene terephthalate, and liquid crystal polyester, polyolefins such as polyethylene, polypropylene, and polybutylene, polyoxymethylene, polyamide, polycarbonate, polystyrene, styrene / acrylonitrile copolymer, and acrylonitrile / butadiene styrene copolymer Polymer, acrylate / styrene / acrylonitrile copolymer, polymethylene methacrylate, polyvinyl chloride,
Polyphenylene sulfide, polyphenylene ether, polyimide, polyamide imide, polyether imide, polysulfone, polyether sulfone, polyether ketone, polyether ether ketone, and the like can be used. Further, these copolymers, modified products and 2
More than one type of blended resin can also be used.
Further, in order to further improve impact resistance, a resin obtained by adding an elastomer or a rubber component to the above resin can be used.

It is preferable that at least a part of the reinforcing fiber 8 is a carbon fiber in order to obtain a lightweight, thin, and good mechanical and electrical characteristics. When fibers other than carbon fibers are used in combination, for example, glass fibers or aramid fibers are preferably used. As the carbon fiber, a polyacrylonitrile (PAN) -based carbon fiber can be used, and a pitch-based carbon fiber can also be used. In order to obtain good mechanical properties, the tensile strength of the carbon fiber alone is preferably in the range of 2,000 to 6,000 MPa, and the tensile modulus is preferably in the range of 100 to 800 GPa.

The carbon fiber in the molded article may be a continuous fiber or a discontinuous fiber, but in order to obtain good mechanical and electrical properties, the carbon fiber has a weight average fiber length of 0.1 to 0.1.
It is important that the range is 1.0 mm. 0.1mm
If it is less than the above, it will not be possible to sufficiently exhibit the properties of carbon fiber such as high strength, high elasticity, and high conductivity. In addition, the fibers are likely to be exposed on the appearance of the surface of the molded product, which is not preferable. In the present invention, the weight average fiber length of the carbon fiber refers to a molded product containing the carbon fiber of 10 × 10 mm.
Then, the cut piece is immersed in a solvent for 24 hours to dissolve the resin component. An optimum solvent is appropriately selected depending on the solvent resistance of the resin.
For example, for nylon, formic acid can be used,
Alternatively, in the case of polycarbonate, dichloromethane or orthochlorophenol can be used.
In the cut piece of the molded product in which the resin component is dissolved, the inorganic component including the reinforcing fiber remains. This is observed with a microscope for 10 to 10
Observe at 0x magnification and select any 4 of the carbon fibers in the field of view.
The fiber length is measured for 00 pieces. Assuming that the fiber length of each carbon fiber is Li, the weight average fiber length Lw in the molded product
Is obtained by the following equation (1).

[0030]

(Equation 1)

The thickness of the molded product is 0.6 to 5.0 mm.
Is preferably within the range. When the wall thickness is less than 0.6 mm, the fibers are easily exposed to the surface of the molded product, and sufficient rigidity cannot be obtained.
It becomes a fragile structure and is unsuitable. When the wall thickness is more than 5.0 mm, sufficient strength and rigidity can be obtained, but irregularities on the surface of the molded product due to the difference in the amount of resin shrinkage become remarkable, making it difficult to obtain a good surface appearance. . In the present invention, the thickness of the molded product is a value obtained by averaging the results of measuring the thickness of the molded product by a micrometer, excluding structural parts such as ribs and bosses.

The carbon fiber content in the molded product is preferably 5 to 40% by weight in order to sufficiently exhibit the mechanical and electrical properties of the molded product while maintaining the moldability. Most preferably, it contains 10 to 30% by weight. In particular, when the content is 10 to 30% by weight, the injection molding can be performed as easily as the molding material containing no reinforcing fiber without impairing the fluidity of the molding material at the time of injection molding, and the molding having a good surface appearance can be obtained. Goods are obtained. In addition, 10
When the content is 30% by weight, extremely excellent elastic modulus, impact resistance and conductivity can be obtained in the molded product as compared with the case where the glass fiber is reinforced only. When the content is less than 5% by weight, the excellent properties of carbon fiber such as elastic modulus, impact strength,
The conductivity cannot be sufficiently exhibited. If the content is more than 40% by weight, the flowability of the fiber-reinforced resin is reduced, adversely affecting the moldability, and the exposure of the reinforcing fibers to the surface of the molded article becomes conspicuous, and the molding having a good appearance is obtained. It becomes difficult to obtain goods. Here, the method of measuring the carbon fiber content of the molded article conforms to JISK 7075.

In order to exhibit high electromagnetic wave shielding properties as a molded product, the volume resistivity of the molded product must be 10 ² Ω · c.
m and a surface resistivity of 10 ⁴ Ω / s
It is preferably within the range of q or less. If each resistance is out of the above range, the conductivity of the molded product is not sufficient and the electromagnetic wave is easily transmitted, and the conduction between the molded product and the fastening member is not sufficient. Similarly, it is preferable that the volume resistivity of the self-tapping screw be within a range of 1 Ω · cm or less and the surface resistivity be within a range of 10 ² Ω / sq or less. If each resistance is outside the above range, conduction between the molded product and the fastening member will not be sufficient. Here, the volume resistivity and the surface resistivity are measured based on ASTM D-257.

Further, in order to maintain a strong fastening and to make the conduction between the fiber-reinforced plastic molded product 20 and the self-tap screw 21 sufficient, the pilot hole diameter d of the boss 7 into which the screw is tightened and the self-tap screw It is preferable that the ratio d / a of the nominal diameter a to the nominal diameter a is in the range of 0.70 to 0.95, and that the thread tip of the self-tapping screw 21 is in contact with the core layer 9 of the boss 7. When d / a is less than 0.70, a vertical crack or a horizontal crack occurs in the boss 7 when the screw is tightened, and the boss is destroyed and the fastening cannot be maintained. When d / a is larger than 0.95, the screw is apt to run idle during or after tightening of the screw, and the tightening cannot be maintained. When the tip of the thread is in contact with the core layer 9 of the boss 7, the screw is gripped by the high-strength and highly-elastic core layer 9, so that a strong fastening is possible and the pull-out strength is improved. .
In addition, the direct contact between the self-tapping screw and the core layer filled with carbon fiber at a high density increases the chance of the screw and the carbon fiber coming into contact with each other and improves the conductivity between the screw and the molded product. . In the case of the metal nut press-fitting method, the resin is heated and melted, then the metal nut is pressed in, the resin is cooled and solidified, and the nut is fixed in the boss.The metal nut is formed of a skin layer with low carbon fiber density In contact with goods. In that respect, the self-tapping method has higher conductivity between the screw and the molded product than the metal nut press-fitting method.

When the ratio L / a between the screwing depth L at which the self-tapping screw is in contact with the prepared hole of the boss for tightening the screw in the axial direction and the nominal diameter a of the screw is within the range of 1.0 to 10. Preferably, there is. If L / a is less than 1.0, sufficient performance in the pulling load and the number of repeated tightening / returning durability cannot be obtained. If L / a is greater than 10, the frictional resistance between the molded product and the screw increases, making the tightening operation difficult, and is not suitable for use as a housing for accommodating an electronic device that requires thinning inside. .

The ratio D / a of the outer diameter D of the boss to which the screw is tightened to the nominal diameter a of the screw is preferably in the range of 1.3 to 5.0. When D / a is less than 1.3, a vertical crack or a horizontal crack occurs in the boss 7 when the screw is tightened, and the boss is destroyed and the fastening cannot be maintained. If D / a is greater than 5.0, sink marks are likely to occur on the back surface of the boss, causing problems in appearance and pressing down the installation space for other components installed in the housing. Not suitable.

It is preferable that the boss for tightening the screw has a chamfered or counterbored shape at the tip of the prepared hole. By providing the shape, the stress concentration at the tip portion of the boss can be reduced, and the fastening between the screw and the molded product can be firmly maintained for a long time. Further, even in the tightening work, the setting of the shape allows the screws on the boss to sit well, thereby improving work efficiency.

The fastening structure of the fiber-reinforced plastic molded article of the present invention is not particularly limited. However, in order to sufficiently exhibit the excellent mechanical and electrical characteristics, which are the characteristics thereof, impact resistance, It is preferable to apply the present invention to a housing for housing electronic devices such as a notebook personal computer, a digital camera, and a mobile phone that require characteristics such as strength, high rigidity, and electromagnetic wave shielding properties.

[0039]

EXAMPLE 1 First, as a reinforcing fiber 8 of a molded article 20 of the present invention, a PAN long fiber carbon fiber bundle (with a tensile strength of 4) was used.
900 MPa, tensile modulus of 230 GPa, number of filaments of 12,000, fineness of 800 TEX, specific gravity of 1.8, volume resistivity of 1.6 × 10 ⁻³ Ω · cm) are passed through a coating die for covering electric wires, and are passed through an extruder for 250. Nylon 6 resin melted at ℃ (weight average molecular weight 15,000)
Was discharged to obtain resin-coated carbon fibers in which the periphery of the carbon fiber bundle was coated with nylon 6 resin. Next, after cooling this resin-coated carbon fiber to room temperature, the strand-cutter was used for 7 mm.
To obtain a long fiber carbon fiber reinforced pellet for injection molding. The carbon fiber content in the pellets is 20% by weight, and the weight average carbon fiber length is 7 mm. The pellets were molded with an injection molding machine having a clamping force of 350 tf,
A 50 mm × 200 mm, 1.5 mm thick injection molded product in the shape of a housing of FIG. 4 was obtained. The thickness of the case-shaped molded product is 1.5 mm. The weight-average fiber length of the carbon fibers in the case-shaped injection-molded article is 0.5 mm.

The volume resistivity of the molded product is 5.0 × 10 ⁻¹ Ω.
Cm, and the surface resistivity was 9.0 Ω / sq.
In addition, two bosses 11 for self-tapping are installed at a pitch of 150 mm in this case-shaped injection molded product. The pilot hole diameter of the boss 11 is φ1.55 (d / a = 0.775), the outer diameter is φ4.0 (D / a = 2.0), and the height is 6 mm. Outer diameter In the prepared hole of the boss 11 of the molded product
"P tight screw", a self-tapping screw manufactured by Nitto Seiko Co., Ltd., using a torque washer "CL-3000" manufactured by Hios Corporation through a steel washer having a thickness of 1 mm.
(L / a = 2.0) to the root of the screw head. Here, the tightening torque and the breaking torque were measured using “HDP5” manufactured by Hios Corporation.
In addition, when the tightening / loosening was repeated at 20 N · cm, the number of repetition durability until the screw stopped functioning was measured. In Example 1, the fastening characteristics of the screws were all good. Further, after tightening the screws to the two bosses 11 via the steel washers, the electric resistance value between the two washers is measured by a digital tester “IWATSU”.
The resistance was 4.0 Ω, and the fastening structure of Example 1 showed high conductivity. <Example 2> Long fiber carbon for injection molding by the same method as in Example 1. A fiber reinforced pellet was obtained, in which the carbon fiber content was 10% by weight, and the weight average carbon fiber length was 7%.
mm. A casing-like injection molded article having the same shape was obtained from the pellets in the same manner as in Example 1. The weight average fiber length of the carbon fibers in the case-shaped injection molded product is 0.5 mm.

The molded product had a volume resistivity of 1.0 Ω · cm and a surface resistivity of 12.0 Ω / sq. Also,
Two bosses 11 for self-tapping are installed at a pitch of 150 mm in this case-like injection molded product. The pilot hole diameter of the boss 11 is φ1.55 (d / a = 0.775), the outer diameter is φ4.0 (D / a = 2.0), and the height is 6 mm.
It is. The self-tapping screw was tightened to the boss in the same manner as in Example 1 (L / a = 2.0), and the screw fastening characteristics and 2
The electrical resistance between two washers was measured. The fastening characteristics of the screw were good, and the resistance value was 10Ω, indicating high conductivity. <Example 3> A long fiber carbon fiber reinforced pellet for injection molding was obtained in the same manner as in Example 1. The carbon fiber content in the pellets was 20% by weight, and the weight average carbon fiber length was 4%.
mm. A casing-like injection molded article having the same shape was obtained from the pellets in the same manner as in Example 1. The weight-average fiber length of the carbon fibers in this case-shaped injection-molded product is 0.3 mm.

The volume resistivity of the molded product is 8.0 × 10 ⁻¹ Ω.
Cm, and the surface resistivity was 10.0 Ω / sq. In addition, two bosses 11 for self-tapping are installed at a pitch of 150 mm in this case-shaped injection molded product.
The pilot hole diameter of the boss 11 is φ1.55 (d / a = 0.775)
, The outer diameter is φ4.0 (D / a = 2.0), and the height is 6 mm. A self-tapping screw was fastened to the boss in the same manner as in Example 1 (L / a = 2.0), and the fastening characteristics of the screw and the electric resistance between the two washers were measured. The screw had good fastening characteristics and a high conductivity of 8 Ω. Comparative Example 1 A long fiber carbon fiber reinforced pellet for injection molding was obtained in the same manner as in Example 1. The carbon fiber content in the pellets was 3% by weight, and the weight average carbon fiber length was 7 m.
m. A casing-like injection molded article having the same shape was obtained from the pellets in the same manner as in Example 1. The weight average fiber length of the carbon fibers in the case-shaped injection molded product is 0.5 mm.

The volume resistivity of the molded product is 3.0 × 10 ³ Ω
Cm, and the surface resistivity is 10.0 × 10 ⁵ Ω / sq.
Met. In addition, two bosses 11 for self-tapping are installed at a pitch of 150 mm in this case-shaped injection molded product. The pilot hole diameter of the boss 11 is φ1.55 (d / a = 0.7
75), the outer diameter is φ4.0 (D / a = 2.0), and the height is 6 mm. A self-tapping screw was fastened to the boss in the same manner as in Example 1 (L / a = 2.0), and the fastening characteristics of the screw and the electric resistance between the two washers were measured. The screw had good fastening characteristics, but exhibited low conductivity of 5 kΩ. Comparative Example 2 A long fiber carbon fiber reinforced pellet for injection molding was obtained in the same manner as in Example 1. After that, the long fiber carbon fiber reinforced pellets for injection molding were manufactured by Nippon Steel Corporation.
The mixture was kneaded and extruded with a shaft extruder “TEX30” to obtain short fiber carbon fiber reinforced pellets for injection molding. The carbon fiber content in the pellets is 20% by weight, and the weight average carbon fiber length is 0.2 mm. Example 1 from the pellet
A housing-like injection molded article having the same shape was obtained in the same manner as in the above. The weight average fiber length of the carbon fibers in the case-shaped injection molded product is 0.08 mm.

The volume resistivity of the molded product is 2.0 × 10 ³ Ω
Cm, and the surface resistivity was 4.0 × 10 ⁵ Ω / sq. In addition, two bosses 11 for self-tapping are installed at a pitch of 150 mm in this case-shaped injection molded product. The pilot hole diameter of the boss 11 is φ1.55 (d / a = 0.77
5), the outer diameter is φ4.0 (D / a = 2.0), and the height is 6 mm. A self-tapping screw was fastened to the boss in the same manner as in Example 1 (L / a = 2.0), and the fastening characteristics of the screw and the electric resistance between the two washers were measured. The screw had good fastening characteristics, but exhibited a low conductivity of 2 kΩ. <Comparative Example 3> A glass fiber bundle cut into a length of 3 mm (tensile strength 3500 MPa, tensile modulus 70 GPa, fineness 130 TEX, specific gravity 2.6, volume specific resistance 10 ¹⁰ Ω · cm or more) was used as the reinforcing fiber 8. Then, the glass fiber bundle and the nylon 6 resin were kneaded and extruded with a twin screw extruder “TEX30” manufactured by Japan Steel Works, Ltd. to obtain short fiber glass fiber reinforced pellets for injection molding. The glass fiber content in the pellets was 20% by weight, and the weight average fiber length of the glass fibers was 0.7 mm. A casing-like injection molded article having the same shape was obtained from the pellets in the same manner as in Example 1.
The weight average fiber length of the glass fibers in this case-like injection molded product is 0.5 mm.

The molded article had a volume resistivity of 10 ¹⁰ Ω · cm or more and a surface resistivity of 10 ¹⁰ Ω / sq or more.
In addition, two bosses 11 for self-tapping are installed at a pitch of 150 mm in this case-shaped injection molded product. The pilot hole diameter of the boss 11 is φ1.55 (d / a = 0.775), the outer diameter is φ4.0 (D / a = 2.0), and the height is 6 mm. A self-tapping screw was fastened to the boss in the same manner as in Example 1 (L / a = 2.0), and the fastening characteristics of the screw and the electric resistance between the two washers were measured. Although the fastening characteristics of the screw were sufficient for both the breaking torque and the number of endurance repetitions, the resistance showed a low conductivity of 20 KΩ or more. <Comparative Example 4> Nylon 6 resin was manufactured by Japan Steel Works, Ltd.
The mixture was kneaded and extruded with a shaft extruder “TEX30” to obtain nylon pellets for injection molding. A casing-like injection molded article having the same shape was obtained from the pellets in the same manner as in Example 1.

The molded product had a volume resistivity of 10 ¹⁰ Ω · cm or more and a surface resistivity of 10 ¹⁰ Ω / sq or more.
In addition, two bosses 11 for self-tapping are installed at a pitch of 150 mm in this case-shaped injection molded product. The pilot hole diameter of the boss 11 is φ1.55 (d / a = 0.775), the outer diameter is φ4.0 (D / a = 2.0), and the height is 6 mm. A self-tapping screw was fastened to the boss in the same manner as in Example 1 (L / a = 2.0), and the fastening characteristics of the screw and the electric resistance between the two washers were measured. The fastening characteristics of the screw were not sufficient for both the breaking torque and the number of endurance repetitions, and the resistance showed a low conductivity of 20 KΩ or more.

Table 1 summarizes the above results.

[0048]

[Table 1]

From Table 1, it can be seen that, as a fastening structure for a fiber-reinforced plastic molded article, in order to obtain high fastening characteristics such as a low tightening torque, a high breaking torque and a high number of repetition durability, a high conductivity between the molded article and the fastening material is obtained. In order to obtain the property, the weight-average fiber length of the carbon fibers contained in the molded product is in the range of 0.1 to 1.0 mm, and the thickness of the molded product is in the range of 0.6 to 5.0 mm. It is necessary that the volume resistivity of the molded product is within the range of 10 ² Ω · cm or less and the surface resistivity is within the range of 10 ⁴ Ω / sq or less. The ratio d / a of the prepared hole diameter d to the nominal diameter a of the screw is in the range of 0.70 to 0.95, the thread tip is in contact with the core layer of the boss, and the screw is tightened. Screw-in where the self-tapping screw is in contact with the prepared hole of the boss in the axial direction. It has been found that the requirement that the ratio L / a of the depth L and the nominal diameter a of the screw be in the range of 1.0 to 10 is necessary.

[0050]

According to the fastening structure of the fiber-reinforced plastic molded article of the present invention, the strength and rigidity are excellent while maintaining the moldability, and the conduction between the parts to be fastened is possible, and the electromagnetic wave shielding property is excellent. It is possible to provide a fastening structure for a molded article made of fiber-reinforced plastic.

[Brief description of the drawings]

FIG. 1 is a sectional view of an embodiment of a fastening structure for a fiber-reinforced plastic molded product according to the present invention.

FIG. 2 is a perspective view of one embodiment of a conventional fastening structure for a fiber-reinforced plastic molded product.

FIG. 3 is a perspective view of one embodiment of a conventional fastening structure for a fiber-reinforced plastic molded product.

FIG. 4 is a perspective view of one embodiment of a fastening structure for a fiber-reinforced plastic molded product according to the present invention.

[Explanation of symbols]

 1: plastic molded product 2: boss 3: metal nut 4: fastening member 5: male screw 6: self-tapping screw 7: boss 8: reinforced fiber 9: core layer 10: skin layer 20: fiber reinforced plastic molded product 21: Self tapping screw 22: Fastening member

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) F16B 5/02 F16B 5 / 02F // B29K 105: 12 B29K 105: 12 B29L 31:34 B29L 31:34 F term ( 3J001 FA02 FA11 GA06 GB01 HA02 JA01 KA19 KA21 KB06 4E360 AB12 AB51 BC05 EA12 ED02 ED27 EE02 FA02 GA11 GA32 GA34 GB46 GC08 4F211 AD05 AD19 AD24 AH42 TA06 TC03 TC16 TD11 TH20 TN76 TQ13

Claims (8)

[Claims] 1. A self-tapping screw is directly tightened into a lower hole of a boss integrally formed as a part of a fiber-reinforced plastic molded product in which a synthetic resin contains at least a reinforcing fiber made of carbon fiber and other members. Characterized by the following conditions [A], [B] and [C]. [A] The weight-average fiber length of the carbon fibers contained in the molded article is in the range of 0.1 to 1.0 mm. [B] The thickness of the molded product is in the range of 0.6 to 5.0 mm. [C] The molded product has a volume resistivity of 10 ² Ω · cm or less and a surface resistivity of 10 ⁴ Ω / sq or less. 2. A structure in which a self-tapping screw is directly screwed into a prepared hole of a boss integrally molded as a part of a fiber-reinforced plastic molded article to enable fastening with another member,
2. The fastening structure for a fiber-reinforced plastic molded product according to claim 1, wherein the following conditions [D] and [E] are satisfied. [D] The ratio d / a of the prepared hole diameter d of the boss for tightening the self-tapping screw to the nominal diameter a of the screw is in the range of 0.70 to 0.95, and the tip of the thread is the core of the boss. Be in contact with the layer. [E] Screw-in depth L at which the self-tapping screw is in contact in the axial direction of the prepared hole of the boss for tightening the self-tapping screw
And the ratio L / a of the screw to the nominal diameter a of the screw is in the range of 1.0 to 10. 3. An outer diameter D of a boss for tightening a self-tapping screw.
3. The fastening structure for a fiber-reinforced plastic molded product according to claim 1, wherein a ratio D / a between the screw diameter and the nominal diameter a of the screw is in a range of 1.3 to 5.0. 4. 4. A molded article having a carbon fiber content of 5-4.
4. The composition according to claim 1, wherein the content is within a range of 0% by weight.
The structure for fastening a fiber-reinforced plastic molded product according to any one of the above. 5. The self-tapping screw has a volume resistivity of 1Ω.
cm or less, and the surface resistivity is 10 ² Ω /
5. It is within the range of sq or less.
The structure for fastening a fiber-reinforced plastic molded product according to any one of the above. 6. The fastening structure for a fiber-reinforced plastic molded product according to claim 1, wherein said molded product is made of a fiber-reinforced thermoplastic resin. 7. A boss for tightening a screw has a chamfered or counterbored shape at a tip end of a prepared hole.
The structure for fastening a fiber-reinforced plastic molded product according to any one of the above. 8. The fastening structure for a molded article made of a fiber-reinforced plastic casing according to claim 1, wherein the molded article houses an electronic device therein.